Thermionic amplifier system



June 24, 1930. B. B. MINNIUM THERMIONIC AMPLIFIER SYSTEM Filed March 2, 1926 1 anon 1 :0;

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BYRON B. MINNIUM, or crrrceoo, trimmers, nssrenon, BY Mnsnn e'ssrenrasnrs, To

STORY & CLARK nnnro come, on onroeeo, rumors, A oonroae'rron or DELA- WARE THERMIONIG AMPLIFIER SYSTEM Application filed March 1926. Serial No. 91,795.

This invention relates to thermionic amplifier systems and more particularly to means for preventing feed-back resulting from the capacity coupling between the elements and circuits of the thermionic tube of a radio frequency amplifier.

It is a general object of the present invention to provide a novel and improved method and means for neutralizing capacity coupling in thermionic amplifiers.

More particularly, it is an object of the present invention to provide a radio frequency amplifier circuit, including an audion or vacuum tube provided with an input circuit and an output circuit, these two circuits being associated by means of a link circuit containing a stopping condenser to prevent the flow of direct current, this link circuit being inductively coupled to either the input circuit, the output circuit, or both, in such a manner that a voltage is impressed on the grid of the tube of a potential equal to and opposite in direction to that resulting from the inherent capacity between the grid and the plate of the tube and the leads from these elements.

Other objects of the present invention will be more apparent to those skilled in the art by a consideration of the accompanying drawings and following specification, wherein are disclosed several exemplary embodi- I ments of the present invention, with the understanding, however, that various changes may be made therein by those skilled in the art without departing from the spirit of the invention or the scope of the appended claims.

The terms audion, vacuum tube and thermionic amplifier which are used synonymously throughout the specification and claims,'refer to any electric amplifying device containing an input electrode, commonly termed a grid; an output electrode re-' ferred to as a plate; and a common electrode, referred to as a filament, wherein the power output is controlled by the input voltage impressed between the grid and the filament.

In the drawings: Figure 1 discloses a simple radio receiving circuit, embodying a single stage of radio frequency amplification and a vacuum tube detector in which the embodied; and I Figures 2 and 8 are similar circuits showing slight modifications.

It is well known that undesirable effects result fron the use of radio frequency amplifiers, due to the capacity coupling between the grid and plate circuits of the vacuum tube, which results in the production of oscillations, sometimes of such strength as to completely mask the incoming signal. In order to overcome the effect of this electrostatic coupling, the present invention contemplates the impressing upon the grid circuit of an electromotive force equal to and opposite in direction to those resulting, by reason of the inherent capacity coupling, between the elements of the tube and their leads, to thereby neutralize the effect of this coupling, the circuits are so arranged that when such potential is once properly adjusted, it is efiective for all frequencies to which the circuits may be tuned,

Referring to Figure 1, there is disclosed an antenna 10 connected to a ground 11,

through the primary 12 of a coupler or're-.

peat coil, the secondary 13 of which is tuned by a shunt connected variable condenser 14,

to the incoming signals. The tuned circuit,

consisting of the secondary 13 and the condenser 14 forms the input circuit to the vacuum tube 15, one end of the tuned circuit being connected to the grid 16 and the other thru inductance 34, to one side of the filament 17. This filament is heated in the usual manner by means of the A battery 18,

present invention is condenser 26 suitably connected between the filament and grid of the tube 2a. The opposite end of the output inductance 22 is connected by means of the wire 27 to the plus side of the B battery 28, the negative terminal of which is connected by means of the wire 29 backto the A battery 18. A suitable by-pass condenser 30 may be provided between the inductance 22 and the filament, to allow a free passage for radio frequency current around the B battery.

The amplifier circuit, as just descri ed, is subject to oscillations, due to the inherent capacity coupling between the grid and plate of the tube and the various portions of the input and output circuits. To neutralize this coupling effect, there is provided a link circuit comprising the inductance 31, the stopping condenser 32 and the inductance 33, all connected in series. The inductance 31 has its remaining end con nected to the wire 27 between the output inductance 22 and the B batter and this coil is in inductive relation to the output inductance. The remaining end of the inductance 33 is connected to the filament circuit and the inductance is coupled to the inductance 34k which is in series between the tuned input circuit 13, 14: and the filament 17 of the vacuum tube v15. T e stopping condenser 32 is of a large capacity and serves only to prevent the flow of direct current from the B battery to the grid, but has no appreciable effect on the flow of radio frequency current.

The coupling effect of the coils 31 and respectively, is such as to produce in the grid circuit a voltage substantially equal and opposite in direction to that induced inthe grid circuit by the capacity coupling between the input and output circuits. Since it is difficult to commercially adjust the number of turns and the coupling be tween the two inductances in the link circuit so as to produce complete neutralization, resort may be had to an auxiliary variable condenser, two of which, 35 and 36, are shown in dotted lines. But a single one of these condensers is used, being placed in either of the indicated positions, depending upon whether or not the voltage from the link circuit is greater or less than that necessary to secure complete neutralization.

The operation of the detector circuit will be obvious from the drawing, and need not be further described. It is believed that the operation of the neutralizing circuit will be apparent from the above description, but it should be noted that this neutralizng circuit is not dependent for its operation upon voltage induced upon the opposite plates of a condenser at'radio frequency, for the.

link circuit offers no appreciable capacitative impedance to the flow of radio frequency currents.

In Figure 2, the circuit arrangements are substantially identical with those disclosed in Figure 1, with the exception that the link circuit is directly connected to the output circuit at 37 between the output inductance 22 and the B battery 28, there being no coupling between these circuits at this junction. Coupling is however resorted to for the purpose of modifying the potential from the plate or output circuit so as to impress the proper potential on the input circuit. This may be done by coupling the coils 33 and 3%, as has been shown in Figure 1. This allows the potential of the point 3. to be modified so that a suitable voltage is applied to the input circuit, by the proper proportioning of the coupling ratio between inductances 33 and 34, and this is the method used in the circuit of Figure 2.

In Figure 2 the stopping condenser 30 around the B battery has been omitted, and suitable radio frequency choke 38 has been inserted in the output circuit to prevent fiow of radio frequency currents through the B battery.

In Figure a further modification is disclosed, wherein the link circuit is coupled, by means of the coil 31, to the output circuit and connected directly to the input circuit between the junction 39 of the condenser 14 and secondary 13 and the inductance 34:. Here again the proper potential is impressed on the input circuit at the point 39 to neutralize the results of inherent capacity coupling between the input and output circuits, by taking the potential of the point 37 and bringing it to a suitable neutralizing potential by adjusting the ratio of coupling between the coils 22 and 31.

The circuit of Figure 3 has omitted the stopping condenser 30 and the radio frequency choke 38, which are in the nature of refinements and not entirely necessary for the operation of the circuit.

It will be seen from the above that three methods are provided for connecting a link circuit between the output circuit and the input circuit to present a direct path for radio frequency current from one circuit to another, with means for insuring the impressing of the proper potential on the input or grid circuit to neutralize the capacity between input and output circuits. l'n both Figures 2 and 3, the auxiliary condensers 35 and 36 perform the same function as explained in connection with Figure l, where one, but not both, are user. These condensers are made variable in order that absolute balance may be obtained.

As shown and described, each form of the invention involves inductance in the input circuit of the first stage of amplification, such as the inductance 34: in each of the three forms of the invention shown, and by this is meant, of course, inductance other than and in addition to the inductance 13 which is in the input circuit of each form of the invention.

In each form of the invention, it will be seen that the inductance 3 21: is in series with the secondary 13 in the input circuit, and that in each form or" the invention the link circuit inductance (31 or 38) is connected through capacity 32 with one terminal of the inductance 34, as shown in Fig. 1 or Fig. 2 or Fig. 3 of the drawings.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a radio receiving apparatus, in combination, a vacuum tube having filament, a grid and a plate, a source of plate potential, an output circuit between said source and plate, a tuned input circuit having a secondary and an inductance therein and connected to said grid and filament, which inductance is excluded from the output circuit, and a link circuit having inductance therein connected through capacity with one terminal of said first mentioned inductance and connecting said input circuit and said output circuit and having coupled relation with at least one of said circuits.

2. In a radio receiving apparatus, in combination, a vacuum tube having a filament, a grid and a plate, a source of plate potential, an output circuit between said source and plate, a tuned input circuit having a secondary and an inductance therein and connected to said grid and filament, which inductance is excluded from the output circuit, and a link circuit having inductance therein connected through capacity with one terminal of said first mentioned inductance and connecting said input circuit and said output circuit and having coupled relation with one of said circuits, said link circuit being of such capacity as to oiier substantially no impedance to the flow therein of radio frequency currents.

3. In a radio receiving apparatus, in combination, a vacuum tube having a filament, a grid and a plate, a tuned input circuit having a secondary and an inductance therein and having one end connected to said grid and the other end to said filament, which inductance is excluded from the output circuit, a source of plate current, an output inductance between said source and the plate, and a link circuit having inductance therein connected through capacity with one terminal of said first mentioned inductance, said capacity being a condenser of large capacity, said link circuit forming a radio frequency path between the tuned circuit and the plate circuit.

4. In a radio receiving apparatus, in combination, a vacuum tube having a filament, a grid and a plate, a tuned input circuit having'a secondary and an inductance therein and having one end connected to said grid, and the other end to said filament, which inductance is excluded from the output circuit, a source of plate current, an output inductance connected at one end to said plate andiat one end to a source of plate current, and a link circuit having inductance therein connected through capacity with one ter, minal of said first mentioned inductance and adapted to freely pass only radio frequency current, said link circuit being so associated with the input and output circuits as to applyto the grid a potential equal and opposite to that due to the capacity coupling of said grid and plate.

5. In a radio receiving apparatus, in combination, a vacuum tube having a filament, a grid and a plate, a tuned input circuit including a secondary and having one end connected to said grid and having an inductance in series with the secondary and connecting the other end of said tuned circuit to said filament, which inductance is excluded from the output circuit, a source of plate current, an output inductance con necting said source to said plate, and a link circuit having inductance therein, non-conductive to direct current, said link circuit associating said inductances.

6. In a radio receiving apparatus, in combination, a vacuum tube having a filament, a grid and a plate, a tuned input circuit including a secondary and having one end connected to said grid and having an inductance in series with the secondary and connecting the other end of said tuned circuit to said filament, which inductance is excluded from the output circuit, a source of plate current, an output inductance connecting said source to said plate, and a link circuit having inductance therein, non-conductive to direct current associating with said inductances, and being coupled to one of them.

7 In a radio receiving apparatus, in combination, a vacuum tube having a filament, a grid and a plate, a tuned input circuit including a secondary and having one end connected to said grid and having an inductance in series with the secondary and connecting the other end of said tuned circuit to'said filament, which inductance is excluded from the output circuit, a source of plate current, an output inductance connecting said source to said plate, and a link circuit having inductance therein, non-conductive to direct current, said link circuit connecting said tuned circuit to said output circuit, and being coupled to oneflof said inductances.

8. In a radio receiving apparatus, in combination, a vacuum tube having a filament, a grid and a plate, a tuned input circuit including a secondary and having one end connected to said grid and having an inductance in series with the secondary and connecting the other end of said tuned circuit to said filament, which inductance is excluded from the output circuit, a sourceof plate current, an output inductance connecting said source to said plate, and a link circuit having inductance therein, non-conductive to direct current, said link circuit connecting said tuned circuit to said output circuit, and being coupled to both of said inductances.

In testimony whereof I hereunto aflix my signature.

BYRON B. MINNIUM. 

